Generalized valence-bond calculations suggest that atomic oxygen chemisorbed on Ni(100) leads to two distinct low-lying states: (1) the radical state with $R_{\perp }=0.88\mathrm{}$ Å and ${\omega }_{\perp }=55\mathrm{}$ meV and (2) the surface oxide state with $R_{\perp }=0.26\mathrm{}$ Å and ${\omega }_{\perp }=38\mathrm{}$ meV. We suggest that the radical state dominates for $p(2\mathrm{}\times 2)$ and that the oxide state dominates for $c(2\mathrm{}\times 2)$. We find that atomic H, Cl, and S lead to only one low-lying state.

• Received 15 January 1981

DOI:https://doi.org/10.1103/PhysRevLett.46.1635